Power converter having capacitors for data transmission

ABSTRACT

A power converter with secondary side regulation (SSR) for driving one or more output loads having capacitors (preferably Y-capacitors) for feedback and data transmission is disclosed. The power converter includes a transformer with primary and secondary windings, a primary circuit, a secondary circuit comprising a secondary controller, and a data transmission circuit comprising a plurality of capacitors. The primary circuit comprises one or more switching means and a primary controller. The secondary circuit is isolated from the primary circuit by the transformer and connected to the output loads and the secondary winding. The data transmission circuit connects the secondary circuit to the primary circuit for transmitting a feedback signal through to become a primary side feedback signal. The capacitors comprises one or more first capacitors on a feedback path and one or more second capacitors on a ground path.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is the U.S. national stage application ofinternational application PCT/CN2019/105993 filed Sep. 16, 2019, whichinternational application was published on Mar. 25, 2021 asInternational Publication WO 2021/051240 A1.

TECHNICAL FIELD

The present disclosure generally relates to power converters for drivinglight emitting diodes (LED) or other output loads. In particular, thepresent disclosure is directed to switched mode power converters withsecondary side regulation (SSR) having Y-capacitors for feedback anddata transmission from the secondary circuit to the primary circuit.

BACKGROUND

Switched mode power converters (also referred to as “power converters”)are commonly used to provide regulated load currents to drive outputloads especially for light emitting devices. The switched mode powerconverters are often configured to isolate the output load from theinput power, such as an alternating current (AC) main or a directcurrent (DC) input voltage, and generate a conditioned DC output voltagefor driving the output load. In the traditional isolated power convertertopologies, output voltage regulation is usually performed with asecondary side feedback using an opto-coupler to electrically isolateand optically couple feedback information to the primary side.

One example of a conventional switched mode power converter with SSR fordriving one or more light emitting diodes (LEDs) using opto-coupler forfeedback and data transmission is shown in FIG. 1. For simplicity andclarity of illustration, common and well-understood elements (such asEMI filter, bridge rectifier, buffer, output rectifier, and smoothingcapacitors) may not be depicted in FIG. 1 to facilitate a lessobstructed view of the depicted features. The power converter 100receives an input signal 101, which may be a DC voltage or a rectifiedsignal from an AC main. The input signal 101 is coupled to a transformer140 comprising a primary winding 141 and a secondary winding 142. Aswitching transistor 131 is configured to control the primary winding141 of the transformer 140, such that current is induced in thesecondary winding 142 of the transformer 140, which can isolate theoutput load from the primary circuit. The output current can be used todrive one or more output loads by connecting the output load to theVOUT+ 151 and VOUT− 152 ports.

In order to stabilize the output voltage at the secondary side, it iscommon to use an opto-coupler 110 to electrically isolate and opticallycouple feedback information from the secondary circuit to the primarycircuit. Generally, the output signal at VOUT+ 151 is processed by avoltage divider 121 having two or more resistors. From the voltagedivider 121, a voltage is generated for powering the secondarycontroller 120. The secondary controller 120 is configured to sense theoutput voltage and/or inductor current continuously, and couple afeedback signal to the primary controller 130 via an opto-coupler 110 toadjust the relative duty cycle of the switching transistor 131. FIGS. 2Aand 2B show the waveforms of the feedback signals captured at theprimary side and the secondary side of the opto-coupler 110,respectively. Therefore, the feedback signal from the secondarycontroller 120 can be coupled to the primary controller 130.

In conventional switched mode power converters, electrical isolation anddata transmission are typically realized by the opto-coupler 110.However, in outdoor and industrial applications, higher surge voltage isexpected between the primary side and the secondary side. The suddenrise in voltage may cause considerable damage to the components in thepower converter. The AC main should be well protected with a highersurge requirement between the live/neutral (L/N) and the protectiveearth (PE). For example, if a surge voltage of >12 kV is expectedbetween the primary side and the secondary side, then the surgerequirement between the L/N and PE is at least 10 kV. However, astandard opto-coupler 110 available can only support up to 8 kV surgevoltage. The cost of a specially designed opto-coupler 110 with highersurge voltage is significantly higher than a standard opto-coupler 110.This is not preferred for general and low-cost applications, such asoutdoor LED devices and other industrial equipment.

In view of the deficiency of conventional switched mode powerconverters, there is a need in the art to have a switched mode powerconverter with SSR for driving LEDs or other output loads without theneed of an opto-coupler. Particularly, feedback and data transmissionfrom the secondary circuit to the primary circuit can be implementedusing conventional passive components such that the system cost of thepower converter can be reduced without any compromise on its performanceor its safety. Furthermore, any noise and error in associated with thedata transmission are also eliminated by a data encoding protocol.

SUMMARY

Provided herein is a power converter with SSR having capacitors,preferably Y-capacitors, for feedback and data transmission from thesecondary circuit to the primary circuit and/or from the primary circuitto the secondary circuit. The power converter comprising a transformer,a primary circuit, a secondary circuit, and a data transmission circuit.The transformer includes a primary winding and a secondary winding. Theprimary circuit comprising at least one switching means coupled to theprimary winding and a primary controller. The secondary circuit isisolated from the primary circuit by the transformer and connected tothe one or more output loads and the secondary winding, and thesecondary circuit comprises a secondary controller. The datatransmission circuit connects the secondary circuit to the primarycircuit for transmitting a feedback signal, and comprises a plurality ofcapacitors, preferably Y-capacitors. The plurality of capacitorscomprises one or more first capacitors on a feedback path and one ormore second capacitors on a ground path. The feedback signal istransmitted through the plurality of capacitors to become a primary sidefeedback signal at the primary circuit.

According to certain aspects, the secondary controller couples thefeedback signal to the one or more first capacitors such that theprimary side feedback signal is coupled to the primary controller basedon the feedback signal.

According to certain aspects, the primary side feedback signal is avoltage surge signal comprising a plurality of voltage sparkscorresponding to rising edges of the feedback signal.

According to certain aspects, the secondary controller is configured togenerate the feedback signal digitally encoded by a coding method.According to a further aspect, the coding method is a special Manchestercode, which is characterized in that a transition from a presence of afirst pulse train to an absence of the first pulse train represents alogic 1, and another transition from an absence of a second pulse trainto a presence of the second pulse train represents a logic 0.

According to a further aspect, the first pulse train and the secondpulse train are delivered periodically in a form of a plurality ofpulses for a period in the range of 1 ms to 20 ms.

According to a further aspect, the first pulse train and the secondpulse train are delivered periodically with 100 pulses in 10 ms.

According to certain aspects, the feedback signal is arranged to carry adata packet comprising a start bit, a plurality of data bits, a paritybit, and a stop bit.

According to certain aspects, the data transmission circuit furthercomprises a two-stage voltage amplifier connected between the secondarycontroller and the one or more first capacitors. The two-stage voltageamplifier is a cascade of a common emitter amplifier followed by acommon collector amplifier.

According to certain aspects, the primary controller comprises aninternal comparator, a decoder, and a modulation generator selected fromthe group consisting of a pulse width modulation (PWM) generator, afrequency modulation generator, and a combination thereof.

According to certain aspects, the ground path has two or more secondcapacitors connected in series, and a protective earth is connectedbetween any two adjacently connected capacitors of the two or moresecond capacitors.

According to certain aspects, the secondary controller is configured todetect a value of a negative temperature coefficient (NTC) thermistor inthe secondary circuit or a second value of an external resistor whichdefines a nominal output current to be provided by the power converter.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter. Other aspects and advantages of the present invention aredisclosed as illustrated by the embodiments hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings, where like reference numerals refer to identicalor functionally similar elements, contain figures of certain embodimentsto further illustrate and clarify various aspects, advantages andfeatures of the power converter as disclosed herein. It will beappreciated that these drawings and graphs depict only certainembodiments of the invention and are not intended to limit its scope.The power converter as disclosed herein will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 depicts a simplified circuit diagram of a conventional switchedmode power converter with SSR having an opto-coupler for datatransmission from the secondary circuit to the primary circuit.

FIG. 2A shows the waveform received by the primary controller from theopto-coupler in accordance with the conventional switched mode powerconverter of FIG. 1.

FIG. 2B shows the waveform received by the opto-coupler from thesecondary controller in accordance with the conventional switched modepower converter of FIG. 1.

FIG. 3 depicts a simplified circuit diagram of an isolated switched modepower converter with SSR having capacitors for feedback and datatransmission from the secondary circuit to the primary circuit inaccordance with an exemplary embodiment of the present disclosure.

FIG. 4A shows the waveform received by the primary controller inaccordance with an exemplary embodiment of the present disclosure.

FIG. 4B shows the waveform generated by the secondary controller inaccordance with an exemplary embodiment of the present disclosure.

FIG. 5 depicts the data format of the special Manchester code inaccordance with an exemplary embodiment of the present disclosure.

FIG. 6 is a table showing the data format of the feedback signaltransmitted from the secondary controller to the primary controller inaccordance with an exemplary embodiment of the present disclosure.

FIG. 7 depicts a block diagram showing the data transmission from thesecondary controller to the primary controller in accordance with anexemplary embodiment of the present disclosure.

FIG. 8A depicts a block diagram showing a first arrangement of the powerconverter for transmitting signal from the secondary side to the primaryside in accordance with an exemplary embodiment of the presentdisclosure.

FIG. 8B depicts a block diagram showing a second arrangement of thepower converter for transmitting signal from the primary side to thesecondary side in accordance with an exemplary embodiment of the presentdisclosure.

FIG. 8C depicts a block diagram showing a third arrangement of the powerconverter for transmitting bidirectional signal in accordance with anexemplary embodiment of the present disclosure.

FIG. 9 depicts an exemplary circuit diagram of an isolated switched modepower converter with SSR having capacitors for feedback and datatransmission from the secondary circuit to the primary circuit inaccordance with an exemplary embodiment of the present disclosure.

FIG. 10 depicts another exemplary circuit diagram of an isolatedswitched mode power converter with SSR having capacitors for feedbackand data transmission from the secondary circuit to the primary circuitin accordance with an exemplary embodiment of the present disclosure.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendepicted to scale.

DETAILED DESCRIPTION

The present disclosure generally relates to power converters with SSRfor driving light emitting diodes (LED) or other output loads. Inparticular, the present disclosure is directed to switched mode powerconverters having capacitors (e.g. Y-capacitors) for feedback and datatransmission from the secondary circuit to the primary circuit and/orfrom the primary circuit to the secondary circuit. As the datatransmission can be implemented using conventional passive componentswithout the use of an opto-coupler, the system cost of the powerconverter can be reduced without any compromise on the performance andthe safety standard.

In the following embodiments, the power converter and the system thereofare merely exemplary in nature and are not intended to limit thedisclosure or its application and/or uses. It should be appreciated thata vast number of variations exist. The detailed description will enablethose of ordinary skill in the art to implement an exemplary embodimentof the present disclosure without undue experimentation, and it isunderstood that various changes or modifications may be made in thefunction and arrangement of the circuit described in the exemplaryembodiment without departing from the scope of the present disclosure asset forth in the appended claims.

The benefits, advantages, solutions to problems, and any element(s) thatmay cause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeatures or elements of any or all of the claims. The invention isdefined solely by the appended claims including any amendments madeduring the pendency of this application and all equivalents of thoseclaims as issued.

For simplicity and clarity, relational terms such as “first,” “second,”and the like, if any, are used solely to distinguish one from anotherentry, item, or device, without necessarily requiring any actual suchrelationship or order between such entries, items, or devices. The terms“coupled” and “connected,” along with any variant thereof, are used tocover any coupling or connection, either direct or indirect, between twoor more elements unless otherwise indicated or clearly contradicted bycontext.

Referring to FIG. 3, a circuit diagram of an isolated switched modepower converter in accordance with an exemplary embodiment of thepresent disclosure is depicted. For simplicity and clarity ofillustration, common and well-understood elements (such as EMI filter,bridge rectifier, buffer, output rectifier, and smoothing capacitors)may not be depicted in FIG. 3 to facilitate a less obstructed view ofthe depicted features. The power converter 200 receives an input signal201 at the primary side for driving the output load at the secondaryside. The input signal 201 may be a DC voltage or a rectified signalfrom an AC main. In case of a DC voltage, the power converter 200 mayreceive an DC input of a e.g. 400V DC which may be provided by an activepower factor correction circuit (PFC) e.g. a boost PFC. In case of arectified signal, the power converter 200 may receive an AC input of a120V/60 Hz AC power, a 220V/50 Hz AC power, or other suitable AC power.The AC input may be rectified by a full bridge rectifier or a halfbridge rectifier to obtain the rectified signal. On the secondary side,output load is connected to the VOUT+ 251 and VOUT− 252, which maycomprise one or more light emitting devices or other output loads. Incase of a light emitting device, the device can be a solid-state devicethat converts electrical energy to light, such as a device comprisingone or more LEDs, an LED string, an LED array, or any combinationthereof. Alternatively, the light emitting device can be a gas dischargelamp, an incandescent lamp, a lighting panel, a low-voltage halogenlamp, or the like, or any combinations thereof. In order to drive theoutput load, a driving current (I_(OUT)) is supplied thereto.

The input signal 201 is coupled to a transformer 240 comprising aprimary winding 241 on the primary circuit and a secondary winding 242on the secondary circuit. The transformer 240 is used to step up or stepdown the input signal 201 and to isolate the AC main from the circuit onthe secondary side. The switching means 231 is configured to control theprimary winding 241 of the transformer 240, such that current is inducedin the secondary winding 242 of the transformer 240. The primary winding241 is magnetically coupled to and isolated from the secondary winding242 by an isolation boundary 243, which can isolate the output load fromthe primary circuit.

To provide enhanced accuracy on the output current, various SSR schemesmay be implemented. As implied by the name, SSR is a scheme involvingsensing the output voltage at the secondary side and comparing thesensed output voltage to a reference voltage for determining an errorvoltage. The error voltage is processed in the secondary controller 220and converted into a feedback signal, which is transmitted to theprimary controller 230 for controlling the at least one switching means231. The feedback signal of the present disclosure is not limited to anerror voltage or a pure feedback from the output of the power converter200, but may be any signal sensed on the secondary side of the powerconverter 200. The switching means 231 may be metal oxide semiconductorfield-effect transistor (MOSFET), bipolar junction transistor (BJT) orany other switching device known to those skilled in the art. In certainembodiments, the switching means 231 is an NMOS transistor and is drainconnected to the primary winding 241 of the transformer 240. The gate ofthe switching means 231 is controlled by the primary controller 230. Thetransformer 240 operates in a discontinuous conduction mode. When theswitching means 231 is switched off, the current in the primary winding241 collapses. The switching means 231 is controlled to provide powerconversion, such that the current from the input signal 201 is regulatedthrough the transformer 240 and induced to the secondary winding 242with a driving current (I_(OUT)) that can be accurately controlled.

The output signal at VOUT+ 251 is processed by a voltage divider 221having at least two or more resistors. The resistors used in the presentdisclosure may be a thin film resistor, a surface mounted chip resistor,or any other type of resistor known to those skilled in the art. Fromthe voltage divider 221, a voltage for powering the secondary controller220 is generated by tapping the two or more resistors at an intermediatelocation.

The secondary controller 220 is configured to sense the output voltageand/or inductor current continuously, and transmit a feedback signal tothe primary controller 230. Advantageously, the power converter 200 doesnot have an opto-coupler for feedback and data transmission from thesecondary circuit to the primary circuit. Instead, the power converter200 comprises a data transmission circuit 210 connecting the secondarycircuit to the primary circuit. The data transmission circuit 210comprises a plurality of Y-capacitors 211, 212, 213, 214. A Y-capacitorused for the present disclosure is a capacitor with sufficient voltagerating to safely span the isolation boundary 243 between the primarycircuit and the secondary circuit of the power converter 200. Generally,Y-capacitors can be used for suppressing the high frequencyelectromagnetic interference (EMI) between the primary side and thesecondary side. In certain embodiments, the Y-capacitors may bepolarized electrolytic capacitors, such as aluminum electrolyticcapacitors or tantalum electrolytic capacitors. The voltage rating ofthe capacitors should be selected to correspond to the operating voltageof the power converter 200. There are at least one or more firstY-capacitors 211, 212 on a feedback path 216 across the isolationboundary 243 and one or more second Y-capacitors 213, 214 on a groundpath 217 across the isolation boundary 243.

The data transmission circuit 210 further comprises a two-stage voltageamplifier 226 connected between the secondary controller 220 and the oneor more first Y-capacitors. The output of the two-stage voltageamplifier 226 is connected to the feedback path 216 on the secondaryside, while the ground of the two-stage voltage amplifier 226 (secondaryground) is connected to the ground path 217 on the secondary side. Thetwo-stage voltage amplifier 226 is a cascade of a common emitteramplifier followed by a common collector amplifier. In the first stage,the common emitter amplifier comprises a first resistor 222 and a firstBJT 223. The base of the first BJT 223 is connected to the secondarycontroller 220 as input, and the collector of the first BJT 223 isconnected to the first resistor 222 and the second stage. In the secondstage, the common collector amplifier (or known as an emitter follower)comprises a second resistor 225 and a second BJT 224. The base of thesecond BJT receives the signal from the first stage, and the emitter ofthe second BJT 224 is connected the second resistor 225 and the feedbackpath 216 across the isolation boundary 243. The common emitter amplifiercan provide a relatively higher input resistance, and the commoncollector amplifier has a low output resistance. Therefore, the use ofthe two-stage voltage amplifier 226 in the data transmission circuit 210can increase the input resistance, lower the output resistance, andachieve large gains. It is easily understood by those skilled in the artthat the two-stage voltage amplifier 226 may be implemented by usingother semiconductor devices or discrete components, such as MOSFET, andbuffer, or by integrating and encompassing within the secondarycontroller 220, a microcontroller (MCU), a custom integrated circuit, afield-programmable gate array (FPGA), or an application specificintegrated circuit (ASIC) to achieve the same advantages withoutdeparting from the purpose and the scope of the present disclosure.

On the feedback path 216 across the isolation boundary 243, the firstY-capacitors 211, 212 are arranged to receive a feedback signal from thesecondary controller 220 and the feedback signal is transmitted throughthe one or more Y-capacitors 211, 212, 213, 214 across the isolationboundary 243 to become a primary side feedback signal, which can be avoltage surge signal or a pulse. The feedback signal provided by thesecondary controller 220 can be a square wave, as shown in FIG. 4B,which defines the characteristics of the modulation signal, e.g. pulsewidth modulation (PWM) signal, for controlling the switching means 231in the primary circuit. However, it is apparent that the feedback signalcannot directly connect to the primary controller 230, and it is notpossible to route a connection from the secondary controller 220 to theprimary controller 230 across the isolation boundary 243. Any attempt intransmitting the exact waveform of the feedback signal to the primarycontroller 230 may require an opto-coupler or other specificallydesigned device(s). The present disclosure advantageously provides amethod for transmitting a primary side feedback signal across theisolation boundary 243. As shown in FIG. 4A, a plurality of voltagesparks is received by the primary controller 230 at the primary circuit.Each voltage spark corresponds to a rising edge on the feedback signal,while the voltage spark corresponds to a falling edge on the feedbacksignal is filtered out by the first diode (D1) 233 and the second diode(D2) 232. The first diode (D1) 233 has a cathode coupled to the feedbackpath 216 at the first Y-capacitor 212, and an anode coupled to theprimary ground. The second diode (D2) 232 has a cathode coupled to theprimary controller 230 and an anode coupled to the feedback path 216 atthe first Y-capacitor 212.

On the feedback path 216, the primary side feedback signal from the datatransmission circuit 210 is coupled to the primary controller 230 basedon the feedback signal from the secondary controller 220. On the groundpath 217, the secondary ground is connected to the primary ground viathe ground path 217 of the data transmission circuit 210. In certainembodiments, the ground path 217 has two or more second Y-capacitors213, 214 connected in series, and a protective earth 215 is connectedbetween any two adjacently connected Y-capacitors (e.g., between 213 and214). Preferably, the protective earth 215 is connected to the case ofthe device having the power converter 200.

With the power converter 200 of the present disclosure, the datatransmission between the secondary side and the primary side is realizedusing a plurality of Y-capacitors. Therefore, by replacing theopto-coupler with the Y-capacitors, the data transmission circuit 210can be implemented with a significantly lower cost. As the Y-capacitorsis a capacitor with sufficient voltage rating to safely span theisolation boundary, which can be used for suppressing the high frequencyelectromagnetic interference (EMI), the power converter 200 can meethigher surge requirement for outdoor and industrial applications.

In order to enable data transmission via the plurality of Y-capacitors211, 212, 213, 214, the secondary controller 220 is configured togenerate the feedback signal digitally encoded by a coding method suchas a special Manchester code described herein. The primary side feedbacksignal from the data transmission circuit 210 has a great deal of noisein a noisy environment or real application device. Unlike thetraditional Manchester code, which cannot effectively distinguishbetween a normal pulse and a noise pulse, the special Manchester codehas strong anti-interference characteristics. The data format of thespecial Manchester code is depicted in FIG. 5. The special Manchestercode is characterized in that a transition from a presence of a firstpulse train to an absence of the first pulse train represents a logic 1,and another transition from an absence of a second pulse train to apresence of the second pulse train represents a logic 0. In certainembodiments, the time period for the pulse train is half of the period(T/2). The first pulse train and the second pulse train are deliveredperiodically by the secondary controller 220 in the form of a pluralityof pulses for a period in the range of 1 ms to 20 ms (T/2=1-20 ms). Inone embodiment, a pulse train having 100 pulses is provided by thesecondary controller 220 with a period (T) of 20 ms. A transition from apresence of a first pulse train having 100 pulses in 10 ms to another 10ms without any pulses represents a logic 1. A transition from 10 mswithout any pulses to a presence of a first pulse train having 100pulses in 10 ms represents a logic 0. It is apparent to those skilled inthe art that the arrangement of the special Manchester code, the numberof pulses, and the period may be modified without departing from thepurpose and the scope of the present disclosure. With the specialManchester code, an acceptable range on the number of pulses is used fordetermining the presence of the pulse train, such that noise couplingmay not cause an error in the data detection.

FIG. 6 further provides a table showing the data format of the feedbacksignal transmitted from the secondary controller 220 to the primarycontroller 230. The feedback signal is arranged to carry a data packet.In certain embodiments, the data packet has 16 bits in length. The mostsignificant bit is the start bit, followed by a reserved bit, aplurality of data bits, a parity bit, and a stop bit. The default valueof the reserved bit is 1. There may be as many as 12 data bits in theexemplary embodiment, and the parity bit is 1 if the data is even. Thestop bit is the least significant bit and the default value of the stopbit is 1. The proposed format of the data packet is one exemplaryarrangement, and it is apparent that the data packet may be arranged inother manners without departing from the purpose and the scope of thepresent disclosure.

Turning now to FIG. 7, a block diagram showing the data transmissionfrom the secondary controller 220 to the primary controller 230 isshown. The primary controller 230 comprises an internal comparator 331,a decoder 332, and a modulation generator 333 (e.g. PWM generator,frequency modulation generator, or a combination thereof). The internalcomparator 331 is configured to eliminate background noise and otherunwanted noise couplings. The decoder 332 is a special Manchester codedecoder configured to decode the received primary side feedback signal.The decoder 332 identifies the presence and absence of the pulse trainin the primary side feedback signal, and determines the logic 1 andlogic 0 in accordance with the data format of the special Manchestercode as detailed in FIG. 5. The decoded result is then used to generatea modulated signal 340 by the modulation generator 333 for controllingthe switching means 231 in the primary circuit to be conducting for aduty cycle as determined by the secondary controller 220. The duty cycleis controlled to regulate an output characteristic of the powerconverter 200, such as an output voltage, a driving current (I_(OUT)),or a combination thereof. In this example, the modulation generator 333is formed by a pulse width modulation (PWM) generator which varies theduty cycle. In an alternative embodiment the modulation generator 333may generate a frequency modulated signal 340, e.g. in case that ahalf-bridge LLC (HB-LLC) converter, as shown in the example of FIG. 10,is controlled.

As demonstrated in FIG. 8A and FIG. 8B, the method for transmitting datavia a plurality of Y-capacitors using the special Manchester code mayalso be applied to data transmission across the isolation boundary 243from the primary controller 230 to the secondary controller 220. Incertain embodiments, the power converter comprises a transformer 240, atransmitting controller 410, a receiving controller 420, and a datatransmission circuit 210. The transmitting controller 410 and thereceiving controller 420 are provided in two circuits isolated from eachother in the power converter. Therefore, the receiving controller 420 isisolated from the transmitting controller 410 by the transformer. Thedata transmission circuit 210 connecting the transmitting controller 410to the receiving controller 420 for transmitting a feedback signal. Thedata transmission circuit 210 comprises a plurality of Y-capacitors anda two-stage voltage amplifier, and the plurality of Y-capacitorscomprises one or more first Y-capacitors on a feedback path and one ormore second Y-capacitors on a ground path. The transmitting controller410 is configured to generate the feedback signal digitally encoded by acoding method such as a special Manchester code. The feedback signal istransmitted through the plurality of Y-capacitors to become a primaryside feedback signal receivable by the receiving controller 420. Thetwo-stage voltage amplifier is connected between the transmittingcontroller 410 and the one or more first Y-capacitors.

With this arrangement, the transmitting controller 410 couples thefeedback signal to the one or more first Y-capacitors such that theprimary side feedback signal is coupled to the receiving controller 420based on the feedback signal. The primary side feedback signal is avoltage surge signal comprising a plurality of voltage sparkscorresponding to rising edges of the feedback signal, while the voltagespark corresponds to a falling edge on the feedback signal is filteredout. The special Manchester code is characterized in that a transitionfrom a presence of a first pulse train to an absence of the first pulsetrain represents a logic 1, and another transition from an absence of asecond pulse train to a presence of the second pulse train represents alogic 0. In certain embodiments, the first pulse train and the secondpulse train are delivered periodically by the transmitting controller410 in the form of a plurality of pulses for a period in the range of 1ms to 20 ms (T/2=1-20 ms). In one embodiment, a pulse train having 100pulses is provided by the transmitting controller 410 with a period (T)of 20 ms. The feedback signal is arranged to carry a data packet. Incertain embodiments, the data packet has 16 bits in length. The mostsignificant bit is the start bit, followed by a reserved bit, aplurality of data bits, a parity bit, and a stop bit.

Referring to FIG. 8C, the transmission is not limited to aunidirectional communication, and in certain embodiments, the powerconverter may comprise two data transmission circuits 530, 630 forachieving a bidirectional communication between the primary side and thesecondary side. On the primary side, there is a first transmittingcontroller 510 and a second receiving controller 620. On the secondaryside, there is a first receiving controller 520 and a secondtransmitting controller 610. The first transmitting controller 510 isconfigured to generate a first feedback signal, which is transmittedthrough the first data transmission circuit 530 to become a firstprimary side feedback signal. Similarly, the second transmittingcontroller 610 is configured to generate a second feedback signal, whichis transmitted through the second data transmission circuit 630 tobecome a second primary side feedback signal.

FIG. 9 depicts an exemplary circuit diagram of an isolated switched modepower converter 200 for a lighting system with SSR having capacitors(e.g. Y-capacitors) for feedback and data transmission from thesecondary circuit to the primary circuit. The power converter 200 isused in a lighting system for driving one or more light emittingdevices, preferably for outdoor applications. The light emitting devicecan be a solid-state device that converts electrical energy to light,comprise one or more LEDs, an LED string, an LED array, or anycombination thereof. The secondary controller 220 is an MCU configuredto detect a value of an external NTC thermistor or a second value of anexternal resistor (not shown in FIG. 9) which defines a nominal outputcurrent to be provided by the power converter 200, and send the value tothe primary circuit via a plurality of Y-capacitors (C2, C5 on thefeedback path and C3, C6 on the ground path). A feedback signal issensed on the secondary side of the power converter 200 by the NTC, andtransmitted to the primary circuit as a primary side feedback signal.The primary controller 230 is configured to receive the primary sidefeedback signal and generate a PWM signal for controlling the twoswitching means 231 in the primary circuit.

FIG. 10 depicts another exemplary circuit diagram of an isolatedswitched mode power converter 700 for a lighting system with SSR havingcapacitors (e.g. Y-capacitors) for feedback and data transmission fromthe secondary circuit to the primary circuit. The power converter 700 isbased on a combination of a boost PFC followed by a LLC convertercomprising two switching means, which is used in a lighting system fordriving one or more light emitting devices, preferably for outdoorapplications. The power converter 700 may receive a supply voltage 705,which may be a DC voltage or an AC voltage from an AC main. The supplyvoltage 705 is filtered and rectified by an EMI filter and arectification block 745. The rectified voltage from the output of theEMI filter and the rectification block 745 is provided to the active PFCcircuit 750, e.g. a boost PFC, which provides a DC input of a e.g. 400VDC as input signal 701 to the following DC-DC-converter which is aHB-LLC converter comprising a transformer 740 having a primary winding741, a secondary winding 742, and two switching elements 731, 739 inthis example. The light emitting device can be a solid-state device thatconverts electrical energy to light, comprise one or more LEDs, an LEDstring, an LED array, or any combination thereof. On the secondary side,output load is connected to the VOUT+ 751 and VOUT− 752, which maycomprise one or more light emitting devices or other output loads. Thesecondary controller 720 is an MCU configured to detect a value on thesecondary side of the transformer 740 e.g. the current and/or voltageprovided to the light emitting device, by a output sensing block 721and/or a value of an external resistor 795 which may define the nominalLED current to be provided by the power converter 700, and send thevalue to the primary circuit via a plurality of Y-capacitors (not shownhere but similar to the Y-capacitors 211, 212, 213, 214) by the datatransmission circuit 710. The primary controller 730 is configured toreceive the feedback signal and to forward this information about thefeedback signal to the control block PFC and HB-LLC control 760 whichmay be an ASIC or other control IC to generate a pulsed signal forcontrolling the switching means 731 and 739 in the primary circuit. Theprimary controller 730 and the PFC and HB-LLC control 760 may be alsointegrated in to one integrated circuit, e.g. as ASIC ormicrocontroller. The primary controller 730 may be configured to receivecontrol bus signals, e g dimming commands like digital addressablelighting interface (DALI) bus commands, via an interface 770.

The isolated switched mode power converter 700 further comprises aprimary side low voltage supply 780 and a secondary side low voltagesupply 790.

In the present disclosure, a detailed description of an isolatedswitched mode power converter with SSR for powering one or more outputloads is provided. It is easily understood by those skilled in the artthat power supplies using various isolated topologies, such as DC to DCconverter, half-bridge resonant converter, forward converter, flybackconverter, and other transformer-based power converters, can alsoimplement the data transmission using a plurality of Y-capacitors basedon a special Manchester code as feedback to achieve the same advantageswithout departing from the purpose and the scope of the presentdisclosure. The power converter may be SSR or primary side regulation(PSR), as long as a data tranmission across the isolation boundary isrequired.

The present disclosure may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiment is, therefore, to be considered in all respects asillustrative and not restrictive. The scope of the disclosure isindicated by the appended claims rather than by the precedingdescription, and all changes that come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A power converter with secondary side regulation (SSR) for drivingone or more output loads such as light emitting diodes (LEDs), the powerconverter comprising: a transformer including a primary winding and asecondary winding; a primary circuit comprising one or more switchingmeans coupled to the primary winding and a primary controller; asecondary circuit being isolated from the primary circuit by thetransformer and connected to the one or more output loads and thesecondary winding, the secondary circuit comprising a secondarycontroller; and a data transmission circuit connecting the secondarycircuit to the primary circuit for transmitting a feedback signal, thedata transmission circuit comprising a plurality of capacitors; wherein:the plurality of capacitors comprises one or more first capacitors on afeedback path and one or more second capacitors on a ground path; andthe feedback signal is transmitted through the plurality of capacitorsto become a primary side feedback signal at the primary circuit.
 2. Thepower converter of claim 1, wherein the plurality of capacitors are aplurality of Y-capacitors.
 3. The power converter of claim 1, whereinthe secondary controller couples the feedback signal to the one or morefirst capacitors such that the primary side feedback signal is coupledto the primary controller based on the feedback signal.
 4. The powerconverter of claim 1, wherein the primary side feedback signal is avoltage surge signal comprising a plurality of voltage sparkscorresponding to rising edges of the feedback signal.
 5. The powerconverter of claim 1, wherein the secondary controller is configured togenerate the feedback signal digitally encoded by a coding method. 6.The power converter of claim 5, wherein the coding method is a specialManchester code.
 7. The power converter of claim 6, wherein the specialManchester code is characterized in that a transition from a presence ofa first pulse train to an absence of the first pulse train represents alogic 1, and another transition from an absence of a second pulse trainto a presence of the second pulse train represents a logic
 0. 8. Thepower converter of claim 7, wherein the first pulse train and the secondpulse train are delivered periodically in a form of a plurality ofpulses for a period in the range of 1 ms to 20 ms.
 9. The powerconverter of claim 7, wherein the first pulse train and the second pulsetrain are delivered periodically with 100 pulses in 10 ms.
 10. The powerconverter of claim 1, wherein the feedback signal is arranged to carry adata packet comprising a start bit, a plurality of data bits, a paritybit, and a stop bit.
 11. The power converter of claim 1, wherein thedata transmission circuit further comprises a two-stage voltageamplifier connected between the secondary controller and the one or morefirst capacitors.
 12. The power converter of claim 11, wherein thetwo-stage voltage amplifier is a cascade of a common emitter amplifierfollowed by a common collector amplifier.
 13. The power converter ofclaim 1, wherein the primary controller comprises an internalcomparator, a decoder, and a modulation generator selected from thegroup consisting of a pulse width modulation (PWM) generator, afrequency modulation generator, and a combination thereof.
 14. The powerconverter of claim 1, wherein the ground path has two or more secondcapacitors connected in series, and a protective earth is connectedbetween any two adjacently connected capacitors of the two or moresecond capacitors.
 15. The power converter of claim 1, wherein thesecondary controller is configured to detect a value of a negativetemperature coefficient (NTC) thermistor in the secondary circuit or asecond value of an external resistor which defines a nominal outputcurrent to be provided by the power converter.
 16. A power convertercomprising: a transformer; a transmitting controller; a receivingcontroller being isolated from the transmitting controller by thetransformer; and a data transmission circuit connecting the transmittingcontroller to the receiving controller for transmitting a feedbacksignal, the data transmission circuit comprising a plurality ofcapacitors; wherein: the plurality of capacitors comprises one or morefirst capacitors on a feedback path and one or more second capacitors ona ground path; and the feedback signal is transmitted through theplurality of capacitors to become a primary side feedback signalreceivable by the receiving controller.
 17. The power converter of claim16, wherein the plurality of capacitors are a plurality of Y-capacitors.18. The power converter of claim 16, wherein the transmitting controllercouples the feedback signal to the one or more first capacitors suchthat the primary side feedback signal is coupled to the receivingcontroller based on the feedback signal.
 19. The power converter ofclaim 16, wherein the primary side feedback is a voltage surge signalcomprising a plurality of voltage sparks corresponding to rising edgesof the feedback signal.
 20. The power converter of claim 16, wherein thesecondary controller is configured to generate the feedback signaldigitally encoded by a special Manchester code.
 21. The power converterof claim 20, wherein the special Manchester code is characterized inthat a transition from a presence of a first pulse train to an absenceof the first pulse train represents a logic 1, and another transitionfrom an absence of a second pulse train to a presence of the secondpulse train represents a logic
 0. 22. The power converter of claim 21,wherein the first pulse train and the second pulse train are deliveredperiodically in a form of a plurality of pulses for a period in therange of 1 ms to 20 ms.
 23. The power converter of claim 16, wherein thefeedback signal is arranged to carry a data packet comprising a startbit, a plurality of data bits, a parity bit, and a stop bit.
 24. Thepower converter of claim 16, wherein the data transmission circuitfurther comprises a two-stage voltage amplifier connected between thetransmitting controller and the one or more first capacitors.
 25. Thepower converter of claim 16, wherein the receiving controller comprisesan internal comparator, a decoder, and a modulation generator selectedfrom the group consisting of a pulse width modulation (PWM) generator, afrequency modulation generator, and a combination thereof.